I use Herald of fire and Added fire damage. These really work amazing with The Consuming Dark becaause 30% of my fire damage gets converted to chaos damage. So no reflect problems and my poison becomes bigger. With more chaos damage I also leech more from Atziri's Promise.
As defenses I use Blasphemy + Enfeeble + Temporal Chains.
Temporal chains also increases the duration of the poison on enemies.

Was thinking of an EK poison build as well, but this is really not the way to go. Such small portion of your damage gets to poison and you lose quite a lot of dps by using Consuming Dark vs a good rare.

You should try building around Cospri's Will Assassin's Garb (or Poison support gem), that would be much more efficient since all your physical damage gets to poison that way, but I guess you are invested a lot to back up to a life build now, so Id suggest just continue building CI EK and forget poison.